The Galveston County Daily News reports a coroner this week ruled the death of 10-year-old Jonathan Singer was a homicide.
Police on Wednesday arrested Tina Madrid of Texas City on a murder charge. Online jail records Thursday did not list an attorney for Madrid, whose bond is $50,000.
Authorities say her son had cerebral palsy and was neglected. His body was discovered last April in his father's vehicle in Spring Branch.
Jeffrey Singer last spring was charged with injury to a child causing serious bodily injury. Prosecutors say his son drowned after Singer allegedly put him in a bathtub and then left to go to a store.
